U.S. patent application number 15/689879 was filed with the patent office on 2018-03-01 for near-bit tool attitude measurement while drilling apparatus and method.
The applicant listed for this patent is Institute of Geology and Geophysics, Chinese Academy of Sciences. Invention is credited to Wenxuan CHEN, Qingyun DI, Jianguang LIU, Yuntao SUN, Yongyou YANG, Wenxiu ZHANG, Jian ZHENG.
Application Number | 20180058192 15/689879 |
Document ID | / |
Family ID | 58079794 |
Filed Date | 2018-03-01 |
United States Patent
Application |
20180058192 |
Kind Code |
A1 |
ZHANG; Wenxiu ; et
al. |
March 1, 2018 |
NEAR-BIT TOOL ATTITUDE MEASUREMENT WHILE DRILLING APPARATUS AND
METHOD
Abstract
A near-bit tool attitude MWD apparatus includes measurement
sensors and a measurement circuit. The measurement sensors transmit
measured signals to the measurement circuit, and the measurement
circuit processes and calculates the signals to obtain attitude
data. The measurement sensors include a triaxial accelerometer, a
triaxial gyroscope, a triaxial magnetic sensor and a temperature
sensor, the measured data of the triaxial accelerometer, the
triaxial gyroscope and the triaxial magnetic sensor are
respectively corrected using the measured data of the temperature
sensor, a first attitude angle is calculated using the corrected
measured data of the triaxial accelerometer and the triaxial
magnetic sensor. Quaternions are initialized using the first
attitude angle, and the initialized quaternions are subjected to
time updating according to the measured data of the triaxial
gyroscope, and further an attitude angle is calculated utilizing
the updated quaternions. The quaternions are periodically
initialized to eliminate cumulative errors of the triaxial
gyroscope, so as to improve the near-bit tool attitude MWD
accuracy.
Inventors: |
ZHANG; Wenxiu; (Beijing,
CN) ; DI; Qingyun; (Beijing, CN) ; CHEN;
Wenxuan; (Beijing, CN) ; YANG; Yongyou;
(Beijing, CN) ; SUN; Yuntao; (Beijing, CN)
; ZHENG; Jian; (Beijing, CN) ; LIU; Jianguang;
(Beijing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Institute of Geology and Geophysics, Chinese Academy of
Sciences |
Beijing |
|
CN |
|
|
Family ID: |
58079794 |
Appl. No.: |
15/689879 |
Filed: |
August 29, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 17/16 20130101;
E21B 7/04 20130101; G01V 11/002 20130101; E21B 47/07 20200501; E21B
47/024 20130101 |
International
Class: |
E21B 47/024 20060101
E21B047/024; G01V 11/00 20060101 G01V011/00; E21B 47/06 20060101
E21B047/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2016 |
CN |
201610772580.5 |
Claims
1. A near-bit tool attitude measurement while drilling (MWD)
apparatus, comprising: a plurality of measurement sensors coupled
to a measurement circuit, wherein the plurality of measurement
sensors include a triaxial accelerometer, a triaxial gyroscope, a
triaxial magnetic sensor, and a temperature sensor, wherein the
measurement circuit comprises a plurality of low-pass filters
coupled to an analog-to-digital converter, a field programmable
gate array coupled to the analog-to-digital convertor, a processor
coupled to the field programmable gate array, a memory coupled to
the processor, and wherein each of the triaxial accelerometer, the
triaxial gyroscope, the triaxial magnetic sensor, and the
temperature sensor is coupled to one of the plurality of low-pass
filters.
2. The near-bit tool attitude MWD apparatus according to claim 1,
wherein the triaxial accelerometer, the triaxial gyroscope and the
triaxial magnetic sensor are arranged in an X axis, a Y axis, or a
Z axis that are orthogonally to each other, and in each axial
direction, directions of sensitive axes of the accelerometer, the
gyroscope and the magnetic sensor are parallel.
3. The near-bit tool attitude MWD apparatus according to claim 1,
wherein high-frequency interferences in analog signals outputted by
measurement sensors are filtered out by the low-pass filters, the
filtered output signals of the measurement sensors are subjected to
acquisition by the analog-to-digital converter, and the timing
control of the analog-to-digital converter is realized by a field
programmable gate array, while the field programmable gate array
performs digital filtering on acquired original data, and sends it
to the processor according to a communication protocol after
packetizing, the processor stores original time series data in the
memory, while the attitude angle is solved, and the processor
comprises an attitude angle calculation module, a quaternion
initialization module and a quaternion updating module.
4. The near-bit tool attitude MWD apparatus according to claim 1,
wherein the accelerometer is a micro electromechanical system
(MEMS) accelerometer, the gyroscope is a MEMS gyroscope, and the
magnetic sensor is a magnetoresistive sensor.
5. The near-bit tool attitude MWD apparatus according to claim 1,
wherein the memory stores calibration coefficients of the
accelerometer, the magnetic sensor and the gyroscope.
6. The near-bit tool attitude MWD apparatus according to claim 1,
wherein the attitude angle comprises an inclination angle, an
azimuth angle, and a toolface angle.
7. A near-bit tool attitude measurement while drilling method,
comprising: (1) measuring data of a triaxial accelerometer, a
triaxial gyroscope, a triaxial magnetic sensor and a temperature
sensor by utilizing the apparatus according to claim 1; correcting
measured data of the triaxial accelerometer and the triaxial
magnetic sensor by utilizing measured data of the temperature
sensor, respectively, and calculating a first attitude angle by
utilizing corrected measured data of the triaxial accelerometer and
the triaxial magnetic sensor; (2) initializing quaternions by
utilizing the first attitude angle; (3) correcting measured data of
the triaxial gyroscope by utilizing the measured data of the
temperature sensor, performing time updating on initialized
quaternions according to the measured data of the triaxial
gyroscope, and further calculating a second attitude angle by
utilizing updated quaternions; (4) measuring the next set of data
of the triaxial gyroscope, and repeating the step (3) to calculate
a third attitude angle; and (5) after 1 s to 10 s, going to the
step (1), calculating the first attitude angle by reusing the data
of the triaxial accelerometer and the triaxial magnetic sensor,
initializing the quaternions by using the first attitude angle, and
periodically initializing the quaternions to eliminate cumulative
errors of the triaxial MEMS gyroscope.
8. The near-bit tool attitude measurement while drilling method
according to claim 7, further comprising: correcting calibration
coefficients and installation errors of the accelerometer, the
magnetic sensor and the gyroscope by utilizing stored calibration
coefficients of the accelerometer, the magnetic sensor and the
gyroscope.
Description
TECHNICAL FIELD
[0001] The present invention mainly belongs to the field of
measurement while drilling (MWD) in oil and gas exploration, and in
particular relates to a near-bit tool attitude MWD apparatus and
method.
BACKGROUND
[0002] Directional drilling is a technology of directing a wellbore
along a predefined trajectory leading to a subsurface target.
Directional drilling is an important technical means for
sidetracking of an existing well, drilling multilateral wells,
extended reach wells, or horizontal wells. Directional drilling can
be employed to reach locations inaccessible to the drilling rig and
to further develop oil and gas resources economically and
effectively. Directional drilling can significantly improve the oil
and gas production, reduce the cost and time of drilling
operations. In addition it is conducive to protecting the
environment. During the directional drilling process, a
comprehensive knowledge of the wellbore direction and the drill bit
orientation is essential to guarantee proper drilling procedure.
Accurate attitude measurement of a downhole drilling tool not only
ensures efficient drilling for predefined targets but also avoids
collision with other wells in proximity. Thus, in addition to the
conventional bottom hole assembly (e.g., including a drill bit, a
positive displacement motor, a stabilizer, a drill collar, etc.),
the directional drilling tool requires position sensors to measure
the attitude of the downhole drilling tool, including an azimuth
angle (a deviation angle from the north orientation in a horizontal
plane), an inclination angle (a deviation angle from the vertical
direction, also known as a pitch angle) and a toolface angle
(equivalent to a roll angle in navigation).
[0003] With further exploration and development of oil fields,
developing difficult-to-produce deposits, such as thin reservoirs,
fault block reservoirs, marginal reservoirs and remaining
reservoirs have been carried out, and requirements for accurate
trajectory control are also increasing. In order to enlarge the
contact area with oil and gas reservoirs in the wellbore, thereby
increasing the production of oil wells, it is necessary to keep
wellbore trajectory in the reservoir accurately. In order to obtain
trajectory parameters near bit, a distance between downhole
position sensors and the drill bit is important. An attitude
measurement tool based on current MWD technology is installed
behind a steerable tool, and attitude parameters including
inclination, azimuth, toolface angles are measured 8 m to 20 m
behind the drill bit, thus it is difficult to obtain a true
wellbore position at the drill bit and determine the actual
condition of entering the reservoir.
[0004] From the perspective of an attitude angle measurement
principle, the existing MWD system includes two main technical
lines, namely, a MWD system based on magnetic sensors and
accelerometers as well as a MWD system based on gyroscopes and
accelerometers.
[0005] (1) The MWD System Based on Magnetic Sensors and
Accelerometers
[0006] An angle measurement unit of this type of MWD system
consists of three orthogonal accelerometers and three orthogonal
magnetic sensors. Quartz flexible accelerometers are generally
selected as the accelerometers, and fluxgate magnetometers are
generally selected as the magnetic sensors. Measurement results of
the accelerometers are used to calculate the inclination angle and
the toolface angle, and the azimuth angle is obtained using the
inclination angle, the toolface angle and geomagnetic field data.
As a result of reference to the magnetic north to measure an
azimuth, the magnetometers require a clean environment without
magnetic interference. A big problem faced by MWD systems based on
magnetometers is magnetic interference, which mainly includes
magnetic interference of a drill string itself and external
magnetic interference generated by a surrounding environment. The
magnetic interference of the drill string mainly affects the
magnetometer along a direction of a rotation axis of the drilling
tool, while the external magnetic interferences have effects on the
three magnetometers. The external magnetic interference mainly
comes from ferromagnetic casings of a producing well nearby, pyrite
and other strata, solar storms, drilling fluid components, magnetic
hot spots, and the like. The presence of the magnetic interference
negatively affects azimuth measurement accuracy. A conventional MWD
system is usually installed in the middle of a nearly 9-meter-long
non-magnetic drill collar to isolate the magnetic interference of
an upper drill string from the magnetic interference of a lower
drill string as far as possible, but a near-bit attitude measuring
apparatus needs to be installed immediately adjacent to the drill
bit, and the magnetic interference generated by the drill bit and a
steerable drilling tool is more serious than that of the
conventional MWD system.
[0007] (2) The MWD System Based on Gyroscopes and
Accelerometers
[0008] This type of MWD system uses gyroscopes to measure a change
in an angular velocity along a sensitive axis of a sensor, which
has been currently applied in the field of directional drilling. A
gyroscope technology has an advantage in application scenarios
where geomagnetic fields are shielded or magnetic interference is
serious because the magnetic interference does not affect the
performance of the gyroscope. At present, due to instrument sizes,
robustness under vibration and shock condition, gyroscope
measurement accuracy and other factors, the gyroscope technology is
mainly applied in a wireline measurement system, and also has some
restrictions in while drilling application scenarios. The maximum
problem of the MWD system based on gyroscopes and accelerometers is
that larger steady state errors may be introduced due to the larger
output signal drift rate of an angular velocity gyroscope and the
higher divergence angle of an integrated attitude angle. There are
cumulative errors, greater cumulative errors especially in an
underground high-temperature environment, since the output of the
gyroscope increases with measurement time, and the volume and the
reliability difficulty meet hostile operating conditions and a
narrow space near the drill bit.
[0009] In summary, both the MWD system based on magnetic sensors
and accelerometers and the MWD system based on gyroscopes and
accelerometers have limitations in the application scenarios,
especially for near-bit tool attitude measurement, and have
difficulties in complex application environments such as downhole
high temperature, severe vibration and shock, strong magnetic
interference, and limited installation space.
SUMMARY
[0010] In view of the above-mentioned problems, the present
disclosure provides a near-bit tool attitude MWD apparatus and
method, which overcome inherent defects (e.g., a micro inertia
component cumulative error problem and a geomagnetic field
measurement interference problem) existing in a single attitude
measurement method by utilizing a combined attitude measurement
technology, effectively improve the attitude measurement accuracy
of a downhole drilling tool by multi-sensor information fusion,
have the advantages of small size and low power consumption, are
conducive to extend downhole working hours under a battery-powered
condition.
[0011] The present invention is achieved by the following technical
solution:
[0012] a near-bit tool attitude MWD apparatus includes measurement
sensors and a measurement circuit, wherein the measurement sensors
transmit measured signals to the measurement circuit, and the
measurement circuit processes and calculates the signals to obtain
attitude data. The measurement sensor includes a triaxial
accelerometer, a triaxial gyroscope, a triaxial magnetic sensor and
a temperature sensor. The measured data of the triaxial
accelerometer, the triaxial gyroscope and the triaxial magnetic
sensor are respectively corrected using the measured data of the
temperature sensor. An initial attitude angle is calculated using
the corrected measured data of the triaxial accelerometer and the
triaxial magnetic sensor. Quaternions are initialized using the
initial attitude angle, and the initialized quaternions are
subjected to time updating according to the measured data of the
triaxial MEMS gyroscope, and further an attitude angle is
calculated utilizing the updated quaternions. The quaternions are
periodically initialized to eliminate cumulative errors of the
triaxial gyroscope.
[0013] Further, the measurement sensors are installed in an X axis,
a Y axis, or a Z axis orthogonally to each other, respectively. In
each axial direction, directions of sensitive axes of the
accelerometer, the gyroscope and the magnetic sensor remain
parallel.
[0014] Further, the measurement circuit includes an
analog-to-digital converter, a field programmable gate array
(FPGA), a memory, a processor and a number of low-pass filters. The
low-pass filters eliminate high-frequency interferences from output
signals of the triaxial accelerometer, the triaxial gyroscope, the
triaxial magnetic sensor and the temperature sensor, respectively.
The filters have cut-off frequencies that match frequency bands of
the accelerometer, the gyroscope, the magnetic sensor, or the
temperature sensor as well as drilling rotation speeds.
[0015] Further, the measurement circuit is structured as follows:
high-frequency interferences in analog signals outputted by
measurement sensors are filtered out by the low-pass filter, the
filtered output signals of the measurement sensors are subjected to
acquisition by the analog-to-digital converter, and the acquired
timing control is realized by the FPGA, while the FPGA performs
digital filtering on the acquired original data, and sends it to
the processor according to a communication protocol after
packetizing, the processor stores original time series data in the
memory, while the attitude angle is solved, and the processor
includes an attitude angle calculation module, a quaternion
initialization module and a quaternion updating module.
[0016] Further, the memory stores calibration coefficients of the
accelerometer, the magnetic sensor and the gyroscope.
[0017] Further, the accelerometer is a MEMS accelerometer, the
gyroscope is a MEMS gyroscope, and the magnetic sensor is a
magnetoresistive sensor.
[0018] Further, the triaxial accelerometer, the triaxial gyroscope,
the triaxial magnetic sensor and the temperature sensor are
measured in a synchronous acquisition mode.
[0019] Further, the attitude angle includes an inclination angle,
an azimuth angle, and a toolface angle.
[0020] Further, the apparatus is installed in a mud channel at the
center of a drill collar or installed on the surface of the drill
collar in a slotting manner.
[0021] A near-bit tool attitude MWD method includes the following
steps: correcting measured data of a triaxial accelerometer, a
triaxial gyroscope, and a triaxial magnetic sensor utilizing
measured data of a temperature sensor, respectively, and
calculating a first attitude angle utilizing the corrected measured
data of the triaxial accelerometer and the triaxial magnetic
sensor, initializing quaternions utilizing the first attitude
angle, and performing time updating on the initialized quaternions
according to the measured data of the triaxial MEMS gyroscope, and
further calculating an attitude angle by using the updated
quaternions; and periodically initializing the quaternions to
eliminate cumulative errors of the triaxial MEMS gyroscope.
[0022] Further, the method further includes: correcting calibration
coefficients and installation errors of the accelerometer, the
magnetic sensor and the gyroscope by utilizing the stored
calibration coefficients of the accelerometer, the magnetic sensor
and the gyroscope.
[0023] Further, the time period may be 1 second to 10 seconds, and
is determined according to a rotation speed of the drilling tool
and an updating rate of attitude data.
[0024] The present invention has the advantageous effects:
[0025] (1) based on a combination of micro-inertia components and
magnetoresistive sensors, the size is small, the power consumption
is low, and satisfies requirements for a limited installation space
and longer working time of a battery-powered near-bit tool attitude
measurement apparatus; and
[0026] (2) attitude measurement is implemented by an inertia and
geomagnetism combination, inherent defects (a micro-inertia
component cumulative error problem and a geomagnetic field
measurement interference problem) existing in a single attitude
measurement method can be avoided, and the attitude measurement
accuracy of the downhole drilling tool is effectively improved by
multi-sensor information fusion, and thus the present invention is
suitable for complex drilling measurement application
scenarios.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic diagram showing the installation of a
triaxial accelerometer, a triaxial gyroscope and a triaxial
magnetic sensor;
[0028] FIG. 2 is a circuit diagram of a near-bit tool attitude MWD
apparatus; and
[0029] FIG. 3 is a flow diagram of a near-bit tool attitude MWD
method.
DETAILED DESCRIPTION
[0030] Objectives, technical solutions and advantages of the
present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with accompanying drawings. It should be understood
that specific embodiments described herein are merely illustrative
of the present invention and are not intended to limit the present
invention.
[0031] Rather, the present invention encompasses any alternatives,
modifications, equivalents, and solutions made within the spirit
and scope of the present invention as defined by the claims.
Further, in order to give the public a better understanding of the
present invention, some specific details are described below in
detail in the following detailed description of the present
invention. It will be appreciated by those skilled in the art that
the present invention may be understood without reference to the
details.
Example 1
[0032] A near-bit tool attitude MWD apparatus includes measurement
sensors and a measurement circuit. The measurement sensors transmit
measured signals to the measurement circuit. The measurement
circuit processes and calculates the signals to obtain attitude
data. The measurement sensors include a triaxial accelerometer, a
triaxial gyroscope, a triaxial magnetic sensor, and a temperature
sensor. The measurement sensors are arranged along an X axis, a Y
axis, or a Z axis that are orthogonal to each other. In each axial
direction, the directions of sensitive axes of different sensors
installed remain parallel.
[0033] The measurement circuit includes an analog-to-digital
converter, a field programmable gate array (FPGA), a memory, a
processor, and a number of low-pass filters. The low-pass filters
eliminate high-frequency interferences from output signals of the
triaxial MEMS accelerometer, the triaxial MEMS gyroscope, the
triaxial magnetic sensor, and the temperature sensor,
respectively.
[0034] The circuit of the apparatus is structured as follows:
high-frequency interferences in an analog signal outputted by the
sensor are filtered out by the low-pass filters. For frequency
bands of different sensors and drilling rotation speeds, filters
with cut-off frequencies matching them are employed. Meanwhile, the
low-pass filters coupled with the A/D converter further play a role
of anti-aliasing filtering. The filtered output signals of the
sensors are sent to the analog-to-digital converter. The acquired
timing control is realized by the field programmable gate array
(FPGA). The FPGA performs digital filtering on the acquired
original data, and sends it to an ARM microprocessor according to a
communication protocol after packetizing. The microprocessor stores
original time series data in a FLASH memory, while an inclination
angle, an azimuth angle and a toolface angle are solved.
[0035] As shown in FIG. 2, the original data and a calculation
result are uploaded to a computer through a USB bus, which
facilitates processing and verifying of a complex algorithm. The
microprocessor includes an attitude angle calculation module, a
quaternion initialization module, and a quaternion updating module.
A method for calculating an attitude angle by the microprocessor is
as shown in FIG. 3.
[0036] The apparatus is installed in a mud channel at the center of
a drill collar or installed in a slot on the surface of the drill
collar.
[0037] The near-bit tool attitude MWD method specifically includes
the following steps:
[0038] (1) measuring signals A.sub.x, A.sub.y, A.sub.z of a
triaxial accelerometer, signals M.sub.x, M.sub.y, M.sub.z of a
triaxial magnetoresistive sensor and an output value T of a
temperature sensor;
[0039] (2) respectively performing temperature correction on each
axial direction of the triaxial accelerometer and the triaxial
magnetic sensor utilizing stored temperature calibration
coefficients according to the measured value of the temperature
sensor;
[0040] (3) correcting scale coefficients and installation errors of
the triaxial accelerometer and the triaxial magnetic sensor
utilizing stored calibration coefficients of the triaxial
accelerometer and the triaxial magnetic sensor; a correction
formula of the accelerometer is as follows:
[ a x a y a z ] = [ K x 1 K xy K xz K yx K y 1 K yz K zx K zy K z 1
] .times. ( [ A x A y A z ] - [ K x 0 K y 0 K z 0 ] )
##EQU00001##
[0041] a.sub.x, a.sub.y and a.sub.z are acceleration values after
compensation, A.sub.x, A.sub.y and A.sub.z are originally measured
acceleration values,
K 1 = [ K x 1 K xy K xz K yx K y 1 K yz K zx K zy K z 1 ] , K 0 = [
K x 0 K y 0 K z 0 ] , ##EQU00002##
K.sub.0 and K.sub.1 are correction coefficients, and are read from
a memory in an attitude measurement circuit of the apparatus.
[0042] A correction formula of the magnetic sensor is as
follows:
[ m x m y m z ] = [ S x 1 S xy S xz S yx S y 1 S yz S zx S zy S z 1
] .times. ( [ M x M y M z ] - [ S x 0 S y 0 S z 0 ] )
##EQU00003##
[0043] m.sub.x, m.sub.y and m.sub.z are magnetic field values after
compensation, M.sub.x, M.sub.y and M.sub.z are magnetic field
values before compensation,
S 0 = [ V x V x V z ] , S 2 = [ S x 1 S xy S xz S yx S y 1 S yz S
zx S zy S z 1 ] , ##EQU00004##
and S.sub.0 and S.sub.1 are correction coefficients and are read
from the memory in the attitude measurement circuit of the
apparatus.
[0044] (4) calculating a first attitude angle utilizing the
corrected data of the triaxial accelerometer and the triaxial
magnetic sensor;
.theta. = arctan ( a x 2 + a y 2 a z ) ##EQU00005## .PHI. = -
arctan ( a y a x ) ##EQU00005.2## .PSI. = arctan ( m x * sin .PHI.
+ m y * cos .PHI. - m x * cos .PHI. * sin .theta. + m y * sin .PHI.
* cos .theta. + m z * cos .theta. ) ##EQU00005.3##
[0045] wherein .theta. is an inclination angle, .phi. is a toolface
angle, and w is an azimuth angle;
[0046] (5) initializing quaternions by utilizing the first attitude
angle;
Q = [ q 0 q 1 q 2 q 3 ] = [ cos .psi. 2 cos .theta. 2 cos .PHI. 2 -
sin .psi. 2 sin .theta. 2 sin .PHI. 2 cos .psi. 2 sin .theta. 2 cos
.PHI. 2 - sin .psi. 2 cos .theta. 2 sin .PHI. 2 cos .psi. 2 cos
.theta. 2 sin .PHI. 2 + sin .psi. 2 sin .theta. 2 cos .PHI. 2 cos
.psi. 2 sin .theta. 2 sin .PHI. 2 + sin .psi. 2 cos .theta. 2 cos
.PHI. 2 ] ##EQU00006##
[0047] wherein q.sub.0, q.sub.1, q.sub.2 and q.sub.3 represent the
quaternions;
[0048] (6) measuring signals .OMEGA..sub.x, .OMEGA..sub.y,
.OMEGA..sub.z of the triaxial gyroscope and the output signal T of
the temperature sensor, and respectively performing temperature
correction on each axial direction of the signals .OMEGA..sub.x,
.OMEGA..sub.y, .OMEGA..sub.z of the triaxial gyroscope by utilizing
stored temperature calibration coefficients according to the
measured value of the temperature sensor;
[0049] (7) correcting a scale coefficient and an installation error
by utilizing stored calibration coefficient of the gyroscope;
[ .omega. x .omega. y .omega. z ] = [ W x 1 W xy W xz W yx W y 1 W
yz W zx W zy W z 1 ] .times. ( [ .OMEGA. x .OMEGA. y .OMEGA. z ] -
[ W x 0 W y 0 W z 0 ] ) ##EQU00007##
[0050] .omega..sub.x, .omega..sub.y and .omega..sub.z are angular
velocity values after compensation, .OMEGA..sub.x, .OMEGA..sub.y
and .OMEGA..sub.z are originally measured angular velocity,
W 1 = [ W x 1 W xy W xz W yx W y 1 W yz W zx W zy W z 1 ] , W 0 = [
W z 0 W x 0 W y 0 ] , ##EQU00008##
and W.sub.0 and W.sub.1 are correction coefficients, and are read
from the memory in the attitude measurement circuit of the
apparatus;
[0051] (8) performing time updating by using the quaternions, and
calculating new quaternions by solving a differential equation;
[ q . 0 q . 1 q . 2 q . 3 ] = 1 2 [ 0 - .omega. x - .omega. y -
.omega. z .omega. x 0 .omega. z - .omega. y .omega. y - .omega. z 0
.omega. x .omega. z .omega. y - .omega. x 0 ] [ q 0 q 1 q 2 q 3 ]
##EQU00009##
[0052] (9) calculating a second attitude angle according to the new
quaternions;
.theta. = arcsin ( 2 ( q 1 q 3 - q 0 q 2 ) ) ##EQU00010## .PHI. =
arctan ( 2 ( q 2 q 3 - q 0 q 1 ) q 0 2 - q 1 2 - q 2 2 + q 3 2 )
##EQU00010.2## .psi. = arctan ( 2 ( q 1 q 3 + q 0 q 2 ) q 0 2 + q 1
2 - q 2 2 + q 3 2 ) ) ##EQU00010.3##
[0053] (10) measuring the next set of data of the gyroscope, and
repeating the steps (7) to (9) to calculate a third attitude angle;
and
[0054] (11) after 1 s to 10 s, going to the step (1), calculating
the first attitude angle reusing data of the triaxial accelerometer
and the triaxial magnetic sensor, and initializing the quaternions
to eliminate cumulative errors of the gyroscope.
[0055] The near-bit tool attitude MWD method is shown in FIG.
3.
[0056] The near-bit tool attitude MWD apparatus can be packaged on
a chip or as a plurality of chips on a substrate. The apparatus is
installed on a drill collar, e.g., in the center of the drill
collar near the mud channel or in a slot on the surface of the
drill collar. The drill collar is a part of the bottomhole assembly
near the bottom of a drillstring. For example, the drill collar is
installed right above the near-bit stabilizer. In another example,
the drill collar having the near-bit tool attitude MWD apparatus is
less than 6 meters from the drill bit, preferably less than 4
meter, and more preferably less than 3 meters from the drill
bit.
* * * * *